<h1 class="display  mb-4">
     添加
</h1>
<form action="/add"  method="POST">
     <div class="form-group">
          <input  type="text"  name="thing"  
                  class="form-control  form-control-lg"
                  placeholder="默认内容"
          >
     </div>
     <input  type="submit"  value="添加"  class="btn  btn-dark   btn-lg">
     <a  href="/"  class="btn  btn-danger  btn-lg">取消</a>
</form>